The 8th edition of Bergy's Manual of Determinative Bacteriology places Anaplasma marginale in Order Rickettsiales, Family Anaplasmatceae and genus Anaplasma. This intraerythrocytic parasite occurs in association with bovine erythrocytes.
Anaplasmosis, a hemolytic disease of the bovine caused by the blood parasite Anaplasma marginale, has caused major economic losses to diaryman and ranchers. It is an endemic problem that can flare up to epidemic proportions at any time. A. marginale parasitizes bovine red blood cells (RBC) and destroys them, this leading to hemolytic anemia which may cause death, particularly in adult cattle. Cattle which do not die can become carriers of the disease for life, unless properly treated. Efforts have been made to produce a vaccine for anaplasmosis, and a known, currently marketed, vaccine effectively prevents clinical disease in vaccinates; reducing death losses from acute anaplasmosis to almost zero. However, that vaccine is grossly contaminated with bovine RBC fragments, or RBC antigens, which can cause fatal neonatal isoerythrolysis (NI) in the offspring of vaccinated cows. It has been found as a result of experimental work, that the process used to separate the A. marginale from the RBC to prepare the commercial vaccine leaves portions of the RBC contaminated with the organisms. As a consequence, when injected into cattle, the animal not only makes antibodies for the A. marginale but, if the blood type of the cow and that of the vaccine are different, antibodies for the RBC are also made by the cow. This does not adversely affect the health of the cow that has received the vaccine, but it causes the concentration of antibodies against some types of RBC in her colostrum. If the blood type of the nursed calf is the same as the RBC in the vaccine, the colostrum will be loaded with antibodies against the calf's RBC. These antibodies will destroy the calf's RBC, and the calf will die. As a result of this condition, known as neonatal isoerythorlysis, NI, many cattlemen have discontinued the use of this vaccine in their cows. Thus, there exists a pressing need for an improved antigen, and vaccine for the suppression of anaplasmosis, particularly an antigen and vaccine free of erythrocyte antigens that cause NI, and process for the preparation of said antigen, and vaccine.